Patent GB-721822-A (GB)
Title: Improvements in or relating to automatic telephone exchange equipment
Inventor: BROADHURST SIDNEY WALTER
IPC: H04M19/02
Filed: 1949-02-14
Abstract: 721,822. Automatic exchange systems. POSTMASTER GENERAL. Feb. 14, 1949, No. 4050/49. Class 40 (4). [Also in Group XL (c)]. In a register-translator system, the common translator comprises an electronic circuit arrangement which performs translations in response to signals from one or more registers either in turn or simultaneously. In one embodiment (Fig. 2) one lead per translated digit is provided between the code storage device and the translator, but in a second embodiment (Fig. 11) only one lead per code is required, all the translated digits for a code being sent simultaneously in response to a signal over this lead and being selectively received in turn by the pulsing-out equipment. After receiving each digit the pulsing-out equipment releases the translator and seizes it again at the end of the inter-train pause. General arrangement, (Fig. 2). Incoming digits are routed by incoming distributer 1 to code and numerical storage devices 2 and 3 respectively, all these apparatus being of wellknown type, but preferably not employing ratchet-and-pawl-driven switches. When code storage is completed, the incoming distributer 1 opens the gate 4, provided that the outgoing counter 6 is normal and that the end of the outgoing inter-digital pause has been signalled. The next synchronizing pulse emitted by common pulse distributer 5 then passes to a switch circuit 7 which operates a further distributer 8. Assuming that the code storage device 2 is a BC selector, its six wipers are respectively connected to the suppressor grids of six of the tubes of a take-off circuit 9. These take-off tubes have a common output circuit, but are controlled by distributer 8 so that only one tube is operative at any time. The BC selector, set in accordance with the dialled code digits, selects six terminals which are cross-connected to the digit terminals corresponding to the digits of the translated number. The synchronizing pulse causes the distributer 8 to mark the take-off tube corresponding to the first wiper of the BC selector, and to open the output circuit to the outgoing counter 6. Pulses at a frequency of 4 Kc/s are generated by oscillator 10, and trains of from one to fifteen pulses respectively, derived therefrom, are then applied to fifteen digit leads 11 (two only of which are shown), and are fed via the cross-connection field to the code storage devices and thence to the take-off tubes of all directors requiring translations. Pulses corresponding to the take-off tube marked thus pass to the outgoing counter 6. As soon as the counter 6 is moved off normal, the gate 4 is closed. The switch 7 locks until restored by a stop pulse at the end of the pulse cycle. The pulsing-out circuit 12 is then coupled to the common multivibrator circuit 13, which supplies ten impulses per second, and impulses are sent in the outgoing loop and to the outgoing counter 6 simultaneously until the counter reaches its normal condition. The number of impulses sent to line is the complement with respect to sixteen of the number received by the take-off circuit 9. At the end of sending, the timing circuit 14 measures off the interdigital pause and the gate 4 is then re-opened to permit the next synchronizing pulse to initiate the transmission of the second digit. Unused code terminals are connected to negative battery, so that when the take-off tubes are switched to them the outgoing counter is not stepped: no impulses are sent to line, and successive synchronizing pulses step the distributer 8 until the take-off circuit 9 is switched to the first numerical digit lead. The numerical digits are transmitted in like manner, and the distributer 8 then signals the clear-out circuit 15. The circuit 16 provides facilities for calls to manual boards, " code only " signals, and calls to C.C.I. exchanges. Circuit details: Take-off circuit (Fig. 3), distributer (Fig. 4), and switch (Fig. 5). The take-off tubes are arranged in two groups of eight, V0 to V7 and V8 to V15, respectively; the tubes of the two groups are paired, e.g. V1 and V9; and the control grids of each pair are connected to a separate group R1 of three resistors, each of which resistors is connected via terminals T1 to T6 and A1 to A6 to the anode of one of the first six tubes (V21 to V26) of four pairs of tubes V21 to V28 (Fig. 4) which consistute a four stage binary counter circuit. These control grid connections are such that only in two conditions of the counter is any pair of take-off tubes enabled to conduct. The screen grid of each tube of a take-off pair is connected to a different common lead (Fig. 3) and, as one of these leads is made positive for counter conditions 0 to 7, and the other for conditions 8 to 15, only one take-off tube can operate at a time and the take-off tubes are enabled in order as the counter steps from 0 to 15. Provided that code storage is completed, and that the intertrain pause has elapsed, the next synchronizing pulse from the pulse distributer 5 (Fig. 2) applied to terminal T42 (Fig. 5) makes V41 conduct, thus operating the trigger circuit V42, V43. This circuit is not restored until a negative stop pulse is applied to T15 at the end of the pulse cycle. The control grids of V37 and V38 (Fig. 3) are connected via T9 to T10 (Fig. 5), so that, after the receipt of a synchronizing pulse, V37 and V38 are cut off. The anodes of V37 and V39 are connected to potential divider P1 which is such that unless V37 and V39 are simultaneously cut off, the screen grids of V0 to V7 are sufficiently negative to prevent these tubes from conducting. Since V39 remains cut off until the binary counter of Fig. 4 marks a number equal to or greater than eight, the first pulse on the control grid of V37 allows the screen grid potentials of V0 to V7 to rise. Tubes V49 and V50 (Fig. 5) constitute a pulse-shaping circuit and, when V42 conducts, a sharp negative pulse is generated at the anode of V50. This pulse is applied via terminals T11, and T12 (Fig. 4) to the common anode resistance of the first element of the binary counter circuit (Fig. 4), which element then changes over, thus rendering take-off tube V1 (Fig. 3) conducting. The pulse groups D to R (Fig. 1) then appear on the respective digit leads and, depending on the cross-connections employed, on the director storage contacts. These contacts are connected to the suppressor grids of the take-off tubes via terminals S1 to S16, but, as only V1 is conducting, the output circuit repeats only the pulses received by that tube. On the restoration of the trigger pair V42, V43 (Fig. 5) by the following stop pulse, tubes V37, V38 become conducting and all the take-off tubes are cut off. Subsequent synchronizing pulses do not affect V41 until its control grid is made positive at the end of the inter-train pause which follows the transmission of the first translated digit. The remaining translated digits are sent in like manner, the take-off tubes being enabled in turn. If no digit pulses are applied to the suppressor grids of the take-off tubes, no sending takes place, and successive synchronizing pulses step on the distributer until the take-off tube enabled is that associated with the first numerical digit. If a " code only " call is received, the distributer is run on to its seventh position and the register is released. After the distributer has received eight pulses, V27 and V28 change over, whereupon V40 is cut off and V39 conducts. The take-off tubes V8 to V15 are therefore marked by synchronizing pulses 8 to 15. On the sixteenth pulse V0 conducts, and the pulse generated at its anode causes release of the register. Outgoing counter (Fig. 6), and pulsing-out and gating circuits (Fig. 7). The outgoing counter is a four stage binary counter generally similar to that of Fig. 4 and comprises four pairs of tubes V51 to V58 preceded by a pulseshaping circuit (V59, V60) similar to that of Fig. 5. The output of the take-off tubes appearing at T13 (Fig. 3) is applied to T14 and shaped pulses from the anode of V60 drive the counter circuit. The anodes of the oddnumbered counter tubes are connected via T21, T23, T25, and T27 (Fig. 6), T210, T230, T260, and T270 (Fig. 7), and a group of resistors R20 to the control grid of V65. Thus, when the counter is normal, V65 conducts; but as soon as it goes off-normal, V65 is cut off: whereupon V64 conducts and the control grids of V70 (Fig. 7) and V41 (Fig. 5) go negative (T28 wired to T29), thus preventing further synchronizing pulses from affecting the outgoing distributer (Fig. 4). Tubes V69, V70 (Fig. 7) constitute a gate circuit, and only when both are cut off can the trigger circuit V61, V62 be changed over. Since the control grid of V69 is wired via T51 and T50 to that of V42 (Fig. 5), V69 is cut off on the restoration of the trigger pair V42, V43 by the stop pulse, and the gate is therefore opened only when the number to be sent is completely stored in the outgoing counter. Negative pulses supplied by a multivibrator circuit, common to all registers (Fig. 9), are fed to the suppressor grids of V61 and V62 via T30 and T31, and to those of corresponding tubes in all registers. A pulse on T31 occurs 66<2>/3 milliseconds after a pulse on T30, and a following pulse on T30 33<1>/3 milliseconds later. The first pulse on T30 after the gate has been opened cuts off V61, whereupon V62 and V63 conduct; relay PU operates and sends an impulse to line. The next pulse on T31 cuts off V62 and V63; V61 again conducts and the negative pulse generated at its anode is applied via T16 and T17 (Fig. 6) to step the outgoing counter on one step. This cycle is repeated until the outgoing counter reaches its normal position, whereupon V65 conducts and V64 is cut off. This renders V70 conducting and prevents further sending. Inter-train pause circuit: (Fig. 7). This comprises the flip-flop circuit V67, V68 having a time constant of about 800 milliseconds. The negative pul